Amalgams of silver have long been used in tooth restorations, but they contain mercury and may constitute a health hazard and they are expensive and not esthetic. Moreover, because they are not adherent to the tooth, extra large and undercut preparations in the tooth are required, leaving less of the tooth than might be desirable merely to remove carious conditions.
Acrylate resins have found a market particularly where esthetics are important, e.g. repair of anterior teeth. Transfer of acrylate resins to posterior teeth has been largely unsuccessful, since acrylates are glassy polymers at the temperature of the mouth environment, and as such tend to creep under stress and ultimately fail structurally. In addition, application of acrylate resins is fraught with difficulty, including adhesion of the acrylate to the instruments but not to the tooth structure, causing leakage at the restoration margins, inability to syringe the material into the cavity, inability to condense the positioned resin, hardness without toughness in the cured resin, and hydrophobicity alien to natural structures.